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USB charging

Cloughjs

Feb 5, 2023
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I have a powersmith 20w LED work light that uses a 7.4v lithium battery pack made from 4x 18650 batteries. The charger is 120vac (I don’t know what the charger steps the power down to) and I want to convert it to charge from one of the 5v 2amp ports in my car so I don’t have to charge it in the house (I forget to grab it for work) I would also like to integrate a smart charge controller into it
 

kellys_eye

Jun 25, 2010
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The charger WILL have the voltage/current details on it somewhere - post a pic of it.
 

bidrohini

Feb 1, 2023
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You need to know the charging specifications of the battery pack and the charger. Then, you can find a voltage step-down converter that can convert the 5V car port power to the required voltage for charging the battery pack. You may also need to use a smart charge controller.
 

Cloughjs

Feb 5, 2023
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7.4v 5200 mah. I want to use a smart controller and I also want a battery charge display. There is nothing about specific charge rate in the manual that came with the light. Just that it lasts between 2 and 8 hours depending on intensity used.

On the back of the light is the charging port, an out going 5v1a usb charging port to charge other devices, a power switch, a mode switch, and a light that show red while charging and in need of charging and green when fully charged.
 

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Harald Kapp

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Nov 17, 2011
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The charger steps down to 9VDC and 2000ma
Sounds more like the "charger" not being a charger but a 9 V / 2 A power supply with the real charger built into the lamp - which makes sense as the charger in the lamp could check overtemperature of the battery, handle charge balancing etc.
In that case you could use any step-up converter that steps 5 V up to 9 V and is able to deliver 2 A. Or use a step-down converter that steps the car's 12 V down to 9 V using e.g. the cigarette lighter port.

Here's an example of a step-up converter.
Here's an example of a step-down converter.
These cheap modules often come on packs of 3, 5 or more. This way you have a spare if a converter doesn't work. You will need to put the module into an isolated case and add wiring to the input and output ports.

This one is a plug-in for the cigarette ligter port and comes with a barrel jack (selectable from a set of 6 different sizes) at the 9 V end for your lamp. Possibly the layman's best option?
 
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